First measurement of the 7Li(γ,t)4He cross section using mono-energetic γ-ray beams

by Catalin Matei (ELI-NP)

ELI-NP Big Meeting Room

ELI-NP Big Meeting Room


The 7Li(γ, t)4He cross section was measured for the first time using mono-energetic γ-rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source (HIγS) at Duke University in USA. The reaction is important for the primordial Li-problem and for testing our understanding of the mirror alpha-capture reactions 3H(α,γ)7Li and 3He(α,γ)7Be. Most measurements over the last 30 years of the 3H(α, γ)7Li reaction have explored the energy range below Ecm = 1.2 MeV but measurements at higher energies could restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the 7Li(γ,t)4He reaction at HIγS consisted of a large-area annular silicon detector array (SIDAR) from Oak Ridge National Laboratory. Several beam characterization instruments were implemented for determining the spatial, spectral, and power characteristics of the gamma-ray beam. Our 7Li(γ,t)4He cross section results are in disagreement with the previous experimental measurements in the same energy range but the extrapolated S-factor agrees with the adopted value. Details of the experiment at HIγS will be presented together with perspectives for future measurements at ELI-NP.